Hepatitis B virus (hereinafter, referred to as “HBV”), known as the Dane particle, has a spherical feature of 42 nm diameter. The outer envelope contains a large amount of hepatitis B surface antigens and surrounds the inner nucleocapsid composed of 180 hepatitis B core proteins. The nucleocapsid contains HBV genome, polymerase, etc (Summers et al., Proc. Nat. Acad. Sci, 72, 4579, 1975; Pierre Tiollais et al., Science, 213, 406–411, 1981).
Within the HBV genome, the coding region of HBV surface antigens contains three open reading frame start sites which share a common termination codon producing same S domain. Thus, the HBV surface antigens may be classified into three types, i.e., (1) Small HBV Surface Antigen (hereinafter, referred to as “S-surface antigen”), containing only the S domain, (2) Middle HBV Surface Antigen (hereinafter, referred to as “M-surface antigen”), containing the S domain and an additional 55 amino acid domain known as Pre-S2, and (3) Large HBV Surface Antigen (hereinafter, referred to as “L-surface antigen”), containing the Pre-S1 domain as well as the Pre-S2 and S domain. Among the expressed surface antigens, S-surface antigen is about 80% or more.
Subtypes of S-surface antigen were classified according to their properties of antibody recognition. Antigenic domains expressed in all surface antigen were classified as determinant a. The four other subtypes are d or y and w or r. Determinant d has a lysine at residue 122 while y has arginine. Similarly, determinant w has a lysine at residue 160 while r has arginine (Kennedy R. C. et al., J. Immunol. 130, 385, 1983). Thus, serological types can be classified into four subtypes, such as adr, adw, ayr and ayw (Peterson et al., J. Biol. Chem. 257, 10414, 1982; Lars O. Marnius et al., Intervirology, 38, 24–34, 1995).
The S-surface antigen specifically binds to hepatocyte (Leenders et al., Hepatology, 12, 141, 1990; Irina Ionescu-Matiu et al., J. Med. Virology, 6, 175–178, 1980; Swan N. T. et al., Gastroenterology 80, 260–264, 1981; Swan N. T. et al., Gastroenterology, 85, 466–468, 1983; Marie, L. M. et al., Proc. Nat. Acad. Sci. 81, 7708–7712, 1984). And, it has been identified that human hepatic plasma membrane contains target proteins such as apolipoprotein H and endonexin II which specifically bind to S-surface antigen (Mehdi H. et al., J. Virol., 68, 2415, 1994.; Hertogs K. et al., Virology, 197, 265, 1993).
Meanwhile, in developing an useful therapeutic monoclonal antibody, a humanized antibody is preferable because monoclonal antibodies obtained from mice could cause an immune response when applying to human.
The Korean patent publication No. 1999-8650 has recently disclosed a variable region of the monoclonal antibody against a Pre-S1 epitope which solely exists in a L-surface antigen among the three HBV surface antigens (S-, M-, and L-surface antigens), a gene encoding the same, and a humanized antibody using the same. Because the L-surface antigen is only 1˜2% of the expressed surface antigens, however, the L-surface antigen is inappropriate as a target for anti-HBV antibody development for diagnostic as well as therapeutic purposes.